In a wireless network environment, a well-known method of determining the location of a mobile transmitting device (e.g., an 802.11 mobile terminal) is time-difference-of-arrival (TDOA). In a TDOA method, a minimum of three receivers (more may be used) of known position precisely measure the time of arrival of a signal transmitted from the mobile transmitting device. The transmitted signal arrives at the receivers at different times depending on the relative location of the mobile transmitting device with respect to the various receivers. The closest receiver will receive the transmitted signal first, and the farthest receiver will receive the signal last. Between any two of the receivers, the time difference of arrival may be associated with a corresponding difference in distance. This difference defines a hyperbolic curve in physical space along which the mobile transmitting device must be located. A third receiver is then used to generated a different hyperbola. These hyperbolas intersect at the location of the mobile transmitting device. This method of triangulation is known as hyperbolic trilateration.
The radio signals travel at approximately the speed of light (roughly 1 nanosecond per-foot). Therefore extremely accurate timing and synchronization between the timing of the receivers is required in order to determine the position of the mobile transmitting device with any useful accuracy.
One method to synchronize the receivers is to utilize a dedicated timing cable between the receivers and a master clock. However, this solution is expensive and cumbersome.
In cases where the receivers also serve as network devices (e.g., an 802.11b Access Point), a solution is desired which uses the existing Ethernet cabling between the receivers and the network infrastructure to synchronize the clocks of the receiver base stations.